Forming of materials

ABSTRACT

A process for producing an extrusion of small cross section from a workpiece in which the workpiece is subjected to a bulk compressive stress in a container so that the end of the workpiece is forced into a reducing die at the end of the container. The material of the workpiece in the reducing die is subjected to an additional localised compressive stress by a tool member having a working face which is applied to the material of the workpiece in the reducing die. Under the combined compressive stresses the material of the workpiece is formed through a die orifice. In one arrangement a rotary tool member is employed which is moved in a circular path through the workpiece material in the reducing die. In another arrangement the tool member is in the form of a reciprocating punch.

United States Patent 11 1 1111 3,884,062 Green May 20, 1975 [54] FORMING OF MATERIALS 3,286,502 11/1966 Cogan 72/260 9 B 1151 Inventor Derek Lytham 3338 333 351923 iii/ T122 35/28 England 3,538,730 11 /1970 Alexander et a1. 72/60 73 Assignee: United Kingdom Atomic gy 3.563.080 2/1971 Alexander Ct a1. 72/60 Authority, London, England 22 Filed: May 7 1973 Primary Examiner-Richard .1. Herbst I Attorney, Agent, or FirmLarson, Taylor & Hmds [21] Appl. No.: 357,531

Related U.S. Application Data [62] Division of $61. No. 880,127, Nov. 26, I969, [57] ABSTRACT abandoned' A process for producing an extrusion of small cross section from a workpiece in which the workpiece is [30] Forelgn Apphc atlon Pl-lomy Data subjected to a bulk compressive stress in a container Sept. 3, 1969 Un ted K ngdom 43716/69 so that the end of the workpiece is forced into a 111 1969 unfted Klngdmnm- 7409/69 ducing die at the end of the container. The material of 1968 United Klngdomm" 58493/68 the workpiece in the reducing die is subjected to an 1969 unlted Kfngdom 3489/69 additional localised compressive stress by a tool mem- 1969 unlted Klngdom 4996/69 her having a working face which is applied to the ma- 191 1969 Umted Kmgdom 9096/69 terial of the workpiece in the reducing die. Under the combined compressive stresses the material of the [52] U.S. C1. 72/60 workpiece is formed through a die orifice In one [51] Int. Cl. B216 23/08 rangement a rotary too] member is employed which is [58] Fleld of Search 72/41, 60, 68, 71, 256, moved i a circular path through the workpiece mate 72/262, 270, 271, 273; 425/371, 381 rial in the reducing die. In another arrangement the tool member is in the form of a reciprocating punch. [56] References Cited UNITED STATES PATENTS 16 Claims, 23 Drawing Figures 3,126,096 3/1964 Gerard et a1 72/60 mmmmws W f 3,884,062

SHEET OlBF 14 PATENTEU W20 I975 SHEET 12%? 1 PATENIED MAY 2 01975 SHEET MUF I4 fly.

FORMING OF MATERIALS This is a division, of application Ser. No. 880,127 filed Nov. 26, 1969 now abandoned.

BACKGROUND OF THE INVENTION This invention relates to the forming of materials and in particular relates to the forming of a product of re duced cross section from a workpiece by an extrusion process.

In extrusion a workpiece is subjected to pressure in a container so that the workpiece is extruded from the container through an orifice defining the product cross section. Pressure may be applied on the workpiece mechanically, as in conventional extrusion, by a ram act ing on the workpiece in the container. Alternatively, as in hydrostatic extrusion liquid may be pressurised about the workpiece in the container to effect extrusion of the workpiece. 7

One feature which is a practical limitation in carrying out such an extrusion process is that the pressure required to carry out extrusion is dependant on the extrusion ratio, the extrusion ratio being defined as the cross sectional area of the workpiece relative to the cross sectional area of the extruded product.

Even in the case of soft materials very high extrusion ratios (for example in the region of 500 1) can only be achieved by the application of extremely high pressures (for example 150-200 tons per square inch) on the workpiece in the container. The manufacture of containers which can withstand such high pressures is difficult and costly.

It is one of the objects of the present invention to provide a method and apparatus capable of producing extruded products at such high extrusion ratios with the application of only moderate pressure to the workpiece in the extrusion container.

SUMMARY OF THE INVENTION According to the present invention a method of producing from a workpiece a product of reduced cross section comprises applying a compressive stress to the bulk of the workpiece and applying an additional compressive stress at a localised region of the workpiece so that the workpiece is stressed in the localised region to an extent causing it to flow through an orifice defining the product cross section.

The additional compressive stress may be produced in the localised region of the workpiece by applying a tool to the workpiece having a working face of smaller cross section then the workpiece, the tool being moved in a closed cyclic path with the working face of the tool maintained in pressure contact with the workpiece during at least part of the cyclic path so that the material of the workpiece in the localised region forward of the working face of the tool is subjected to an additional compressive stress and is formed through an orifice defining the product cross section.

According to the invention a method of producing from a workpiece a product of reduced cross section also comprises applying pressure to the workpiece so as to set up a compressive stress in the bulk of the workpiece and so as to produce a reduction in cross section in a region of the workpiece, applying a tool having a material working face to said region of the workpiece and moving the'tool so that the material of the workpiece in said region forward of the working face of the tool is subjected to an additional compressive stress and is formed through an orifice defining the product cross section.

In accordance with the invention one form of apparatus for producing a product of smaller cross section from a workpiece comprises a container, pressure means for applying a compressive stress to the bulk of the workpiece within the container, a rotary member with a projecting tool member having a material working face, means for rotating the rotary member so that the tool member is moved in a circular path with the working face of the tool member in pressure contact with the material of the workpiece, whereby the material of the workpiece in the localised region forward of the working face of the tool member is subjected to an additional compressive stress and is formed through an orifice defining the product cross section.

An alternative form of apparatus for carrying out a method according to the invention comprises a container, pressure means for applying a compressive stress to the bulk of the workpiece within the container, a tool in the form of a reciprocable punch and means for reciprocating the punch between limits whereby on the forward stroke of the punch the face of the punch is forced under pressure into the workpiece so that the material of the workpiece in the localised region forward of the face of the punch is subjected to an additional compressive stress and is thereby formed through an orifice leading from the container and whereby on the backward stroke of the punch the compressive stress applied to the bulk of the workpiece feeds the material of the workpiece to replace the material extruded during the previous forward stroke of the punch.

In both the above forms of apparatus the container may have a bore tapered at one end to a reduced cross section, the pressure applied to the workpiece in the container also acting to force the end of the workpiece into the tapered end of the bore of the container and the tool being applied to operate on the material of the workpiece in the tapered end of the bore of the container.

DESCRIPTION OF THE DRAWINGS Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which:

FIG. 1 is a longitudinal sectional elevation of one embodiment of the invention, the area bounded by the chain dotted circle II being along the line I I in FIG. 2.

FIG. 2 is a partial plan view of the arrangement shown in FIG. 1.

FIG. 3 is a detail of FIG. I isometric form.

FIG. 4 is a longitudinal sec tional elevation of a second embodiment of the invention.

FIG. 5 is a detail of FIG. 4 in isometric form.

FIG. 6 is a longitudinal sectional elevation of a third embodiment of the invention.

FIG. 7 is a longitudinal sectional elevation of a fourth embodiment of the invention.

FIG. 8 is a detail of FIG. 7 on a larger scale.

FIG. 9 is a detail showing a modified form of the arrangement shown in FIG. 7.

FIG. 10 is a longitudinal sectional elevation of a fifth embodiment of the invention.

FIG. 11 is a detail showing a modified form of the ar rangement shown in FIG. 10.

FIG. 12 is a longitudinl sectional elevation of a sixth embodiment of the invention.

FIG. 13 is a longitudinal sectional elevation of a seventh embodiment of the invention.

FIG. 14 is a longitudinal sectional elevation of an eighth embodiment of the invention.

FIG. 15 is a detail, in isometric form of the arrangement shown in FIG. 14.

FIG. 16 is a longitudinal sectional elevation of a ninth embodiment of the invention.

FIG. 17 is a longitudinal sectional elevation of a tenth embodiment of the invention.

FIG. 18 shows an eleventh embodiment of the invention in isometric form.

FIG. 19 is a detail, in isometric form, showing a modification of the arrangement of FIG. 18.

FIG. 20, is a detail, in isometric form, showing another modification of the arrangement of FIG. 18.

FIG. 21 is a detail, in isometric form, showing a further modification of the arrangement of FIG. 18.

FIG. 22 is a cross section along the line XXII XXII in FIG. 21.

FIG. 23 is a cross sectional detail showing a fourth modification of the arrangement of FIG. 18.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIGS. 1 and 2 of the drawings there is shown a pressure container 1, having a bore 2. The bore 2 leads to a narrower outlet opening 3 through a curved section 4 at the end of the bore 2. Alternatively the section 4 may be of straight conical taper or instead of being a concave curvature as shown in the drawing may be of convex curvature somewhat as the shape of a trumpet bell. A tubular shaft 5 projects into the opening 3 from outside the container 1. The shaft 5 is supported in the opening 3 by a heavy duty thrust bearing carried by a hydraulic ram (not shown) so that the shaft 5 can be moved into and out of the opening 3. The shaft 5 is arranged to be driven by an electric motor. A die block 6 is mounted on the upper end of the shaft 5. The die block 6 has a transverse key 7 which fits in slots 8 in the upper end of the shaft 5. As shown in FIG. 3 a die support member 9 is formed projecting from the upper face of the die block 6. The die support member 9 has an inclined flat face 10. A housing 11 in the die support member is fitted with a die insert 12. The housing 11 has a conical lead in 13 from the face of the die support member 9 to the mouth of the die insert 12. The die insert 12 is connected with the bore of the shaft 5 by a passageway 14.

In use of the arrangement shown in the drawings a billet 15 (shown in chain dotted outline in FIG. 1) is held in the container 1. Hydraulic liquid in the interspace 16 surrounding the billet 15 is pressurised to apply an overall compressive stress on the billet 15 so that the end of the billet is forced into the curved section 4 at the end of the bore 2 of the container 1. The shaft 5 is rotated to drive the die block 6. The material of the billet 15 forward of the face 10 of the die support member 9 is subjected to an additional localised compressive stress system arising from the mechanical loading applied by the face 10 of the die support member 9 on the billet material, as the die block 6 is rotated. The material of the billet traversed by the die support member during each rotation of the die block 6 is extruded through the die insert 12. Extrusion of the billet material is under the additive effect of the overall compressive stress applied in the billet by pressurisation of the hydraulic liquid about the billet and the localised additional compressive stress which is set up forward of the face 10 of the die support member 9. The extruded wire product passes from the die insert 12 through the passageway 14 and out through the bore of the tubular shaft 5. Extrusion is continuous whilst the shaft 5 is rotated, the billet 15 being fed continuously downwards by the pressure of the hydraulic liquid into the region of the die block 6.

To prevent rotation of the billet 15 in the container 1, the curved section 4 of the container bore 2 may be formed with grooves 17 as shown in FIG. 1, the material of the billet 15 being forced into engagement with the grooves 17.

As disclosed in copending British application No. 30277/64 cognate with 28823/65 a direct mechanical loading may also be applied on the billet 15 by a ram entered into the rear end of the bore 2 of the container 1. The mechanical loading applied by the ram supplements the axial forces feeding the material of the billet into the region of the die block 6 and also contributes to the stress system giving rise to extrusion of the material of the billet through the die insert 12.

Particularly in the case of soft materials the overall compressive stress may be set up in the billet by direct mechanical loading of the billet for example by a ram as in conventional mechanical extrusion.

By way of example an arrangement for extruding a 2% inch diameterlead billet has the following parameters: I

Internal diameter of die insert 12 0.1 inches Ratio of area of face 10 of the die support member to the area of the die insert orifice 4 1 Pressure in hydraulic liquid 4 tons/square in Ratio of area of container bore 2 area to die block 6 The reduction of a 2% inch diameter lead billet to a wire of 0.l inch diameter entails a reduction ratio of 625: l. At the pressure used, i.e., 4 tons per square inch a reduction ratio of only 6 1 could be achieved using simple hydrostatic extrusion. Thus at the same pressures of operation the process of the present invention enables a hundred fold increase in the extrusion ratio which can be achieved. From another point of view in order to achieve a reduction ratio of 625 l in a lead billet by simple hydrostatic extrusion a pressure of tons per square inch would be required. This represents a reduction in pressure in the region of a factor of 10.

As a further example an arrangement capable of handling a 4 inch diameter copper billet would have the following parameters:

Diameter of die insert 12 0.125 inches Ratio of area of face 10 of die support member to area of die insert orifice 9:1

Pressure in hydraulic liquid 50 tons per square in.

Power of drive motor for shaft 5 25 30 I-I.P.

Ratio of bore 2 diameter to die block 6 diameter 4:1

Rate of revolution of shaft 5 200 R.P.M.

In an arrangement having the above parameters a 4 inch diameter billet is reduced to a wire of 0.125 inches diameter. If this were carried out by a simple hydrostatic extrusion process the extrusion ratio entailed would be approximately l000:l and in the case of a copper billet a prohibitively high liquid pressure of 165 tons per square inch would be required for simple hydrostatic extrusion.

Although the invention has its main application to the extrusion of harder metals such as copper it may also be used for the extrusion of softer metals such as aluminium. Although a soft metal such as aluminium can be directly reduced to wire by simple hydrostatic extrusion at practical extrusion pressures use of the invention enables a considerable reduction in pressure with saving in cost of pressure vessels and pressure generating equipment which are expensive items.

In FIGS. 4 and 5 of the drawings there is shown a chamber 21 having a bore 22. A reducing die 23 is screw fitted in the end of the bore 22.

The die 23 is sealed in the bore 22 by a copper mitre ring 24 and a rubber O-ring 25. A sleeve shaped rotary die block 26 is fitted on a stationary stem 27. The end 28 of the sleeve shaped die block 26 is reduced to fit in the parallel outlet 29 of the reducing die 23. A die member 30 is formed projecting from the annular end face 31 of the die block 26. A die orifice 32 in the die member 30 connects with a passageway 33 leading through the sleeve shaped die block 26. The stationary stem 27 has a pointed end 34 with flats 35. The stationary stem 27 is fixedly supported on a main base frame and the sleeve shaped die block 26 is rotatably supported on the stationary stem 27 by a heavy duty bearing (not shown).

In use of the arrangement described above a billet 36 is subjected to the pressure of hydraulic liquid 37 surrounding the billet 36 in the bore 22 of chamber 21. The pressure of the liquid 37 subjects the billet to an overall compressive stress system and also loads the billet 37 longitudinally into the reducing die 23. The nose of the billet 36 is forced into the reducing die 23 over the pointed end 34 of the stationary stem 27. The sleeve shaped die block 26 is driven on the stationary stem 27 thus driving the die member 30 through the billet material at the mouth of the reducing die 23. The material of the billet forward of the face of the die member 30 is subjected to an additional localised compressive stress system arising from the mechanical loading applied on the billet material in the reducing die 23 by the face of the die member 30. The material of the billet traversed by the die member 30 is extruded through the die orifice 32. Extrusion of the billet material is under the additive effect of the overall compressive stress applied in the billet by the pressure of the hydraulic liquid and the localised additional compressive stress which is set up in the billet material at the mouth of the reducing die 23 forward of the face of the die member 30.

The wire product extruded through the orifice 32 passes through the passageway 33 in the die block 26 and is coiled on a spool concentric with the stationary stem 27. Under the pressure of the hydraulic liquid 37 the billet 36 is continually fed into the reducing die 23 to replace the billet material which is extruded through the orifice 32 in the die member 30. The pointed end 34 of the stationary steam 27 acts as a guide for feeding of billet material into the region of the annular end face 31 of the sleeve shaped die block 36. The engagement of the flats 35 on the pointed end 34 of the staionary stem 27 with the end of the billet 36 assists in preventing the billet 36 rotating with rotation of the sleeve shaped die block 26.

The sleeve shaped die block 26 has to be driven under a load sufficient to provide the additional compressive stress in the billet material required to achieve extrusion. In addition part of the driving load applied to the sleeve shaped die block 26 is used in overcoming the friction between the annular end face 31 of the die block 26 and the billet material. As the die block 26 is in frictional contact with the billet material only over the relatively small area of its annular end face 31 only a minor proportion of the driving load applied to the die block 26 is used in overcoming friction.

This is to be compared with the arrangement of FIG. 1 in which the full end face of the die block 6 is in contact with the billet. In the arrangement of FIG. 1 there is a greater loss of power as more redundant work has to be done in overcoming the friction between the full end face of the die block 6 and the billet.

During each rotation of the die block 6 the die member 30 removes a semi toroidal section of the billet ma.- terial. Depending on the mean diameter (D) of the pitch circle of the rotating die member 30, the pressure (P) in the billet material ahead ofthe rotating die member 30 and the shear strength (65) of the billet a maximum area (a) can be defined for the end face of the die member 30 above which the semi toroidal section will shear from the billet instead of extruding. In the case of a die member 30 having an area (a) less than this maximum the semi toroid is clamped i.e., it is of a circumferential length giving a surface area which will not shear.

FIG. 6 shows an alternative arrangement to that shown in FIGS. 4 and 5. In FIG. 6 there is shown a chamber 41 having a bore 42. A reducing die 43 is screw fitted in the end of the bore 42. The die 43 is sealed in the bore 42 by a copper mitre ring 44 and a rubber O-ring 45. A tubular rotary die block 46 has an end part 47 reduced to fit in the parallel outlet 48 of the reducing die 43. A die member 49 is formed projecting from the annular end face 50 of the die block 46. A die orifice 51 in the die member 49 connects with a passageway 52 leading through the die block 46. The other end of the bore 42 of the chamber 41 is closed by a screwed plug 53 which is sealed in the bore 42 by a copper mitre ring 54 and a rubber O-ring 55. A mandrel 56 integral with the screwed plug 53 extends coaxially through the bore 42 of the chamber 41. The lower end of the mandrel 56 extends into the bore 57 of the die block 46. A passageay 58 leads radially through the wall of the chamber 41 into the bore 42. The rotary die block 46 is supported by a heavy duty bearing (not shown).

In use of the arrangement shown in FIG. 6 a tubular billet 59 is fitted on the mandrel 56 in the bore 42 of the chamber 41. Hydraulic liquid 60 surrounding the billet 59 in the chamber 41 is pressurised through the radial passageway 58 in the wall of the chamber 41. The pressure of the liquid 60 subjects the billet S9 to an overall compressive stress system and also loads the billet 59 longitudinally into the reducing die 43. The rotary die block 46 is driven to drive the die member 49 through the billet material at the mouth of the reducing die 43.

The billet material forward of the face of the die member 49 is subjected to an additional localised compressive stress system arising from the mechanical loading applied by the face of the die member 49 on the billet material as the die block 46 is rotated. The material of the billet at the mouth of the reducing die 43 is extruded through the die orifice 51 in the die member 49 under the additive effect of the overall stress applied in the billet material by the pressure of the hydraulic liquid 60 and the localised compressive stress set up in the billet material at the mouth of the reducing die 43 by the loading of the die member 49. The wire product extruded through the die orifice 51 passes through the passageway 52 in the die block 46 and is coiled on an external take up spool. In the arrangement of FIG. 6, as in the arrangement of FIGS. 4 and power losses due to friction between the annular end face of the die block 46 and the billet are reduced as compared with the arrangement of FIGS. 1 to 3 in which the die block 6 has a full circular end face in contact with the billet.

The arrangement shown in FIG. 7 of the drawings comprises a pressure container 61 having a longitudinal bore 62. The container 61 is mounted vertically on a base plate 63 by a flange 64 which is screwed onto a boss 65 at the base of the container 61. The flange 64 is secured to the base plate 63 by threaded studs 66. A reducing die 67 is fitted in the upper end of the container bore 62. A circumferential groove 68 around the outside of the reducing die 67 contains an O-ring 69 which seals the die 67 in the container bore 62. The die 67 seats on a base ring 70 which is screwed into the threaded upper end 71 of the container bore 62 up to the limit of an external flange 72 on the base ring 70. A carrier plate 73 rotatably mounted on the upper end of the container 71 by a thrust bearing 74 is fitted with a holder 75 for a rotary die block 76. As shown in FIG. 8 the reducing die 67 has a parallel outlet 77 and the rotary die block 76 has an end section 78 of reduced diameter fitting in the parallel outlet 77 of the reducing die 67.

The carrier plate 73 is circular and has an outer rim 79 housing the outer race 80 of the thrust bearing 74. The inner race 81 of the thrust bearing 74 is fitted in a circumferential step 82 around the upper end of the container 61. The holder 75 for the rotary die block 76 is cylindrical with a central drilling 83 and is externally threaded to screw into a central aperture 84 in the carrier plate 73. The rotary die block 76 is fitted in a counterbore 85 at the lower end of the central drilling 83 in the holder 75. The rotary die block 76 has longitudinal splines 86 engaging in keyways 87 in the counterbore 85 of the holder 75. The rotary die block 76 has a blind ended bore 88 corresponding to the central drilling 83 in the holder 75. As also shown in FIG. 8 an oblique drilling 89 in the lower end face 90 of the rotary die block 76 houses an extrusion die 91 which partially projects from the lower end face 90 of the rotary die block 76. A smaller diameter extension 92 of the drilling 89 connects with the bore 88 of the rotary die block 76.

Connection of the bore 62 of the container 61 with a pipe 93 for carrying liquid under high pressure is provided by passageway 94 in the container 61 leading from the boss 65 to the bore 62. The pipe 93 is connected with the passageway 94 at the boss 65 by a union nut 96.

Disc shaped weights 97 are stacked on the carrier plate 73 to load the rotary die block 76. The lowermost weight seats in a step 98 around the upper face of the carrier plate 73.

FIG. 7 of the drawings also shows an arrangement for supporting a billet 99 in the bore 62 of the container 61. This billet support arrangement comprises a blind ended nylon sleeve 100 supported by a coil spring 101 which is mounted on a flanged boss 102 at the bottom end of the bore 62 in the container 61.

FIG. 9 of the drawings shows a modification of the arrangement of FIG. 7. In the arrangement of FIG. 9 the rotary die block 76 has a through drilling 103 fitting about a stationary stem 104 which is mounted from a main frame member of the equipment (not shown). The drilling 103 of the rotary die block 76 has a counterbore 105 at its upper end corresponding to the central drilling 83 in the holder 75. A passageway 106 leads from the extrusion die 91 to the counterbore 105 in the rotary die block 76. The lower end 107 of the stationary stem 104 is pointed and projects below the lower end face 90 of the rotary die block 76.

In use of the arrangement shown in FIG. 7 of the drawings liquid 108 surrounding the billet 99 in the bore 62 of the chamber 61 is pressurised to subject the billet 99 to compression. Under the action of the pressurised liquid 48 the billet 69 is subjected to an upward thrust so that the nose of the billet 99 is forced into the reducing die 67. The weights 97 load the carrier plate 73 to hold the rotary die block 76 against the upward thrust of the billet 99. Sufficient of the weights 97 are used so as to slightly overload the carrier plate 73, the majority of the weight acting to resist the upward thrust of the billet 99 on the end face of the rotary die block 76. The assembly of the carrier plate 73, the rotary die block 76 and the weights 97 is rotated bodily. The carrier plate 73 may be driven as shown in FIG. 7 by a V- belt 109 driving a V grooved ring 110 fitted around the rim 79 of the carrier plate 73. Rotation of the die block 76 drives the die member 91 in a circular path through the material at the reduced end face of the billet 99. The billet material in the path of the die member 91 is extruded through the die member 91 and the extruded product emerges from the die member 91 through the extension 92 of drilling 89 and is removed through the bore 88 of the rotary die member 16 and the central drilling 83 in the holder 75.

As the die block 76 is rotated the billet 99 is fed continually upwards into the reducing die 67 to replace the material extruded on each rotation of the die block 76.

The arrangement of FIG. 9 operates in a similar manner except that the rotary die block 76 rotates on the stationary stem 104, the lower pointed end 107 of which penetrates the end face of the billet 99. The extruded product passes from the die member 91 through the longitudinal passageway 106 in the rotary die member 76 and is removed through the counterbore 105 of the rotary die member 76 and the central drilling 83 in the holder 75. In the arrangement of FIG. 8 the sliding friction between the annular end face of the rotary die member 76 and the end face of the billet 99 is less than in the arrangement of FIG. 7 wherein the whole circular end face of the rotary die member 76 is in sliding frictional contact with the end face of the billet 99. Therefore in the arrangement of FIG. 8 the work required to overcome friction between the end face of the rotary die member 76 and the end face of the billet, which requires the use of additional power in driving the rotary die member 76, is less than in the arrangement of FIG. 7. Also in the arrangement of FIG. 8 the lower pointed end 107 of the stationary stem 104 feeds the billet material into the path of the die member 91 and static friction between the lower pointed end 107 of the stationary stem 104 and the end face of the billet 99 assists in preventing rotation of the billet 99 in the chamber 61.

In FIG. of the drawings there is shown a chamber 111 having a bore 112. A reducing die 113 is formed at one end of the bore 112 of chamber 111. A plunger 114 is entered into the other end of the bore 112 of chamber 111. The plunger 114 is sealed in the bore 112 by a copper mitre ring 115 and a rubber O-ring 116. A reciprocable plunger 117 is mounted at the mouth of the reducing die 113 in axial alignment with the bore 112 of the chamber 111. The plunger 117 has a bore 118 which is restricted at its end to form a die orifice In operation of the apparatus shown in FIG. 10 liquid 120 enveloping a billet 121 in the chamber 111 is pressurised by loading the plunger 114. The liquid 120 is held at a constant pressure sufficient to cause extrusion of the end of the billet 111 into the reducing die 113 up to the end face of the plunger 117. However the pressure in the liquid 120 is insufficient to cause extrusion of the billet 111 through the die orifice 119 in the plunger 117. The plunger 117 is loaded against the reduced end face of the billet 121 at the mouth of the reducing die 113 so that the material of the billet 121 is extruded through the die orifice 119 in the plunger 117 as the plunger 117 moves forward into the billet 127 in the direction of the arrow 123.

The material of the billet at the mouth of the reducing die 113 extrudes through the orifice 119 under the additive effect of the overall compressive stress applied in the billet by the pressure of the liquid 120 and the localised additional compressive stress applied at the reduced end of the billet by the mechanical loading of the plunger 117. The plunger 117 is advanced to a forward limit and is then retracted tending to leave a void in the end of the billet of the same diameter as the plunger 117. However as the plunger 117 is retracted the pressure of the liquid 120 acting on the billet 121 feeds the billet 121 forward into the reducing die 113 to close up the void left by withdrawal of the plunger 117. This cycle is repeated until the majority of the bllet 121 has been extruded.

Typically the operating parameters of such a form of apparatus for extrusion of a copper billet are as follows:

Diameter of billet 121 4 inches.

Diameter of plunger 117 at the mouth of the reducing die 113 1 inch.

Diameter of die orifice 119 inch.

Pressure applied in liquid 120, 75 Ton/m Loading of plunger 117 on forward extrusion stroke 70 Tons/m The movement of the plunger 117 will be small, e.g., V4 inches in the example above and the speed of reciprocation will be rapid, e.g., 2 cycles per second.

The limiting condition is reached when the face stress on the plunger 117 during its forward stroke is approximately equal to the pressure in the liquid 110. Higher face stresses will cause leakage of liquid through the reducing die 113. However at this limiting condition the overall extrusion ratio will be approaching the square of the ratio normally possible with simple hydrostatic extrusion at the liquid pressure employed in the present method.

FIG. 11 shows a modified form of apparatus in which the mouth of the reducing die 1 13 leads into a chamber 124. The plunger 117 operates in the chamber 124 and during retraction of the plunger 117 the billet 121 is extruded through the reducing die 113 into the chamber 124 by the pressure of the liquid in the main chamber 111. On the forward stroke of the plunger 117 the material present in the chamber 124 is extruded through the die orifice 119 in the pluger 117.

FIGS. 12 and 13 show further variants of the arrangement shown in FIG. 10.

In FIG. 12 here is shown a chamber 131 having a bore 132. A reducing die 133 is screw fitted in one end of the bore 132 of the chamber 131. The reducing die 133 is sealed in the bore 132 by a copper mitre ring 134 and a rubber O-ring 135. The reducing die 133 has a conical throat 136 leading into a cylindrical section 137. A radial passageway 138 leading from the cylindrical section 137 of the reducing die 133 has an extrusion die orifice 139 formed at its inner end. The radial passageway 138 in the reducing die 133 connects with a corresponding radial passageway 140 in the chamber 131. A reciprocable plunger 141 is entered into the cylindrical section 137 of the reducing die 132.

In operation of the apparatus shown in FIG. 12 liquid 142 enveloping a billet 143 in the chamber 131 is pressurised for example by means of a plunger operating in the bore of the chamber 131 behind the billet 143. The liquid 142 is raised to a pressure sufficient to cause extrusion of the billet through the throat 136 into the cylindrical section 137 of the reducing die 133. However the pressure of the liquid 142 is arranged to be insufficient to cause extrusion of the billet 143 through the die orifice 139. The plunger 141 is reciprocated in the cylindrical section 137 of the reducing die 133. On the forward stroke of the plunger 14] the billet material in the cylindrical section 137 of the reducing die 133 is subjected to an additional compressive stress by the loading of the plunger 141. The billet material in the cylindrical section 137 of the reducing die 133 extrudes through the die orifice 139 under the combined stress system arising from the overall compressive stream applied in the billet material by pressurisation of the liquid 142 about the billet 143 and the additional localised stress applied on the billet material in the cylindrical section 137 of the reducing die 133 by the loading of the plunger 141.

The plunger 141 is advanced to a forward limit and is then retracted. As the plunger 141 is retracted the pressure of the liquid 142 feeds further billet material through the throat 136 into the cylindrical section 137 of the reducing die 133. This cycle is repeated until the majority of the billet 143 has. been extruded. The extruded product passes out through the radial passageways 138 and 140 in the reducing die 133 and the chamber 131.

In FIG. 13 there is shown a chamber 151 having a bore 152. A reducing die 153 is screw fitted in one end of the bore 152 of the chamber 151. The reducing die 153 is sealed in the bore 152 by a copper mitre ring 154 and a rubber O-ring 155. The reducing die 153 has a conical throat 156 leading into a cylindrical section 157. A reciprocable plunger 158 is entered concentrically into the cylindrical section 157 of the reducing die 153. The plunger 158 is of smaller diameter than the internal diameter of the cylindrical section 157 of the reducing die 153. 

1. A method of producing from a workpiece a product of reduced cross section by extruding through an orifice defining the reduced product cross-section, comprising applying an initial bulk compressive stress to the whole of the workpiece to influence the workpiece to extrude through the orifice and applying a tool having a working face of smaller cross section than the workpiece to a localized region of the woRkpiece adjacent the orifice, and moving the tool in a repetitive closed cyclic path with the working face of the tool maintained in pressure contact with the localized region of the bulk-stressed workpiece during at least part of the cyclic path to apply an additional compressive stress at said localized region to influence the localized region to extrude through said orifice, so that the material of the workpiece in the localized region forward of the working face of the tool is subjected to an additional compressive stress and is thereby formed through the orifice defining the product cross section under the influence of the bulk compressive stress acting in combination with the additional compressive stress in the material of the workpiece in the region forward of the working face of the tool.
 2. A method of producing from a workpiece a product of reduced cross section comprising applying pressure to the workpiece in a container having a region of smaller cross-section than the workpiece so as to set up an initial bulk compressive stress in the whole of the workpiece and so as to force a part of the workpiece into the region of smaller cross-section to produce a reduction of cross section in a part of the workpiece, applying a tool having a material working face to said part of the workpiece, and moving the tool relative to the workpiece and relative to said region of the container in a repetitive closed cyclic path with the working face of the tool maintained in pressure contact with said part of the workpiece during at least part of the cyclic path, so that the material of the workpiece in said part forward of the working face of the tool is subjected to an additional compressive stress and is thereby formed through an orifice opening into said region of smaller cross-section and defining the product cross section under the influence of the bulk compressive stress acting in combination with the additional compressive stress in the material of the workpiece in the part forward of the working face of the tool.
 3. Apparatus for producing from a workpiece a product of reduced cross section comprising a workpiece, an orifice defining the reduced product cross-section, means for applying an initial bulk compressive stress to the whole of the workpiece to influence the workpiece to extrude through said orifice, a tool having a working face of smaller cross section than the workpiece, the tool being mounted for application to a localized region of the bulk-stressed workpiece adjacent said orifice and so as to be movable in a repetitive closed cyclic path with the working face of the tool maintained in pressure contact with the workpiece during at least part of the cyclic path, and means for effecting relative movement between the tool and the workpiece to apply an additional compressive stress at said localized region to influence the localized region to extrude through said orifice, whereby the material of the workpiece in the localized region forward of the working face of the tool is subjected to an additional compressive stress and is thereby formed through the orifice defining the product cross section under the influence of the bulk compressive stress acting in combination with the additional compressive stress in the material of the workpiece in the localized region forward of the working face of the tool.
 4. Apparatus for producing from a workpiece a product of reduced cross section comprising a container having a region of smaller cross section than the workpiece, means for applying pressure to the workpiece in the container so as to set up an initial bulk compressive stress in the whole of the workpiece and so as to force a part of the workpiece into the region of smaller cross section of the container, an orifice opening into said region and defining the reduced product cross-section, a tool having a working face and mounted for application of the working face to the part of the bulk-stressed workpiece in said region of smaller cross section of the container, and Means for moving the tool in a repetitive closed cyclic path with the working face of the tool maintained in pressure contact with the workpiece during at least part of the cyclic path so that the material of the workpiece in the region of smaller cross section of the container forward of the working face of the tool is subjected to an additional compressive stress and is thereby formed through the orifice defining the product cross section under the influence of the bulk compressive stress acting in combination with the additional compressive stress in the material of the workpiece in the region of small cross section of the container forward of the working face of the tool.
 5. Apparatus as claimed in claim 3 wherein said means for applying a bulk compressive stress comprises a container, and pressure means for applying a compressive stress to the bulk of the workpiece within the container, said tool comprising a reciprocable punch, and means for reciprocating the punch between limits, the apparatus being constructed and arranged such that on the forward stroke of the punch the face of the punch is forced under pressure into the bulk-stressed workpiece, so that the material of the workpiece in the localized region forward of the face of the punch is subjected to an additional compressive stress and is formed through the orifice leading from the container, and whereby on the backward stroke of the punch the compressive stress applied to the bulk of the workpiece feeds the material of the workpiece to replace the material formed during the previous forward stroke of the punch.
 6. Apparatus as claimed in claim 4 wherein the bore of the container has a tapered end reducing to said smaller cross section, and said means for applying pressure to the workpiece in the container sets up a compressive stress in the bulk of the workpiece so as to force the corresponding end of the workpiece into the tapered end of the bore of the container, said tool comprising a reciprocable punch, and said means for moving the tool comprising means for reciprocating the punch between limits such that on the forward stroke of the punch the face of the punch is forced under pressure into the material of the workpiece in the tapered end of the bore of the container so that the material of the workpiece in the localized region forward of the face of the punch is subjected to an additional compressive stress and is formed through the orifice leading from the tapered end of the container, and such that on the backward stroke of the punch the compressive stress acting in the bulk of the workpiece feeds further material into the tapered end of the bore of the container to replace the material formed during the previous forward stroke of the punch.
 7. Apparatus as claimed in claim 4 wherein the bore of the container has a tapered end leading to a secondary chamber of smaller cross section, and said means for applying pressure to the workpiece in the container sets up a compressive stress in the bulk of the workpiece so as to force the corresponding end of the workpiece through the tapered end of the bore of the container into the secondary chamber, said tool comprising a reciprocable punch, and said means for moving the tool comprising means for reciprocating the punch between limits such that on the forward stroke of the punch the face of the punch is forced under pressure into the material of the workpiece in the secondary chamber so that the material of the workpiece in the secondary chamber is subjected to an additional compressive stress and is formed through the orifice leading from the secondary chamber and defining the product cross section, and such that on the backward stroke of the punch the compressive stress acting in the bulk of the workpiece feeds further material from the workpiece into the secondary chamber through the tapered end of the bore of the container.
 8. Apparatus as claimed in claim 6 wherein the punch is entered axially along the container axis into the said correspondiNg end of the work piece at the forward part of the tapered end of the bore of the container.
 9. Apparatus as claimed in claim 7 wherein the punch is entered axially along the container axis into the said corresponding end of the material of the workpiece in the secondary chamber.
 10. Apparatus as claimed in claim 6 wherein the punch is entered through the side wall of the tapered end generally normal to the bore axis of the container.
 11. Apparatus as claimed in claim 5 wherein the orifice defining the product cross section is provided in the reciprocable punch leading from the face of the punch.
 12. Apparatus as claimed in claim 8 wherein the orifice defining the product cross section is provided in the side wall of the tapered end of the bore of the container.
 13. Apparatus as claimed in claim 10 wherein the orifice defining the product cross section is provided leading axially from the forward end of the tapered end of the bore of the container.
 14. Apparatus as claimed in claim 9 wherein the punch is of smaller diameter than the internal diameter of the secondary chamber and the orifice defining the product cross section is provided by the annular space defined between the punch and the wall of the secondary chamber.
 15. Apparatus as claimed in claim 10 wherein the punch is entered into the tapered end of the bore of the container through a passageway in the wall of the container and the punch is of smaller diameter than the internal diameter of said passageway, the orifice defining the product cross section being provided by the annular space defined between the punch and the wall of the passage way.
 16. Apparatus as claimed in claim 4 wherein said tool comprises a reciprocable punch, and said means for moving the tool comprises means for reciprocating the punch between limits, the apparatus being constructed and arranged such that on the forward stroke of the punch the face of the punch is forced under pressure into the workpiece, so that the material of the workpiece in the localized region forward of the face of the punch is subjected to an additional compressive stress and is formed through the orifice leading from the container, and whereby on the backward stroke of the punch the compressive stress applied to the bulk of the workpiece feeds the material of the workpiece to replace the material formed during the previous forward stroke of the punch. 